(1) Field of the Invention
This invention relates to an improved process and apparatus for treating a gas-liquid-solid effluent stream, and more particularly to an improved process and apparatus for separating into component streams a gas-liquid-solids effluent stream resulting from dental procedures.
(2) Description of the Prior Art
A typical dental effluent stream, i.e. from an oral vacuum tube in a dental application contains water, air and other gases, such as nitrous oxide; lighter than water particles, such as human tissue and heavier than water particles, such as ground tooth particles, filling, etc. Most of such particles, and in particular the larger ones, are separated by a screen and filter bowl assembly at the inlet of a pump, such as a water ring vacuum pump. The smaller particles, water, liquids and gases are drawn into the suction side of the vacuum pump and thereafter discharged from the pump. The effluent liquid and gases may be dumped into a vented drain, or as is more prevalent, primarily because of environment codes, are introduced into an air-water separator to separate liquid from gas, dumping the liquid and smaller suspended lighter and heavier than water particles through a trap into a drain and venting to atmosphere the gases via a separate line. The separation of gas-liquid mixtures is not very effective in present dental applications, and significant liquid including contaminants suspended and dissolved in the liquid may be carried away in the vent stream.
Vacuum evacuation systems, for example, used in some dental or process applications, include vacuum pump assemblies having water rings as the prime mover for creation of vacuum. Such pumps must continuously be supplied with water to lubricate and cool internal seals and provide the "piston" action to alternately draw in and expel the liquid-gas mixture designed to be handled by the water rings of such system.
Additionally, and primarily because of environmental, specifically water conservation, reasons, but also for economic and financial reasons, such water based evacuation systems have recently been equipped with water conservation subsystems, commonly referred to as "water recyclers" or "water recirculators". The useful effect, that of recirculating water in such conservation subsystems, is carried out by extracting from the discharged effluent water stream a portion of that waste water flow and re-introducing this portion of recirculated water into the vacuum pump along with a reduced amount of fresh water flow. The net savings of fresh water is the difference between the water consumption without recirculation and that with recirculation. The recirculated water added to the reduced fresh water flow may or may not add up to an amount equal to 100% of the flow normally introduced into the pump when operating without recirculation.
It is assumed that the state of the art and general operation of the water pump is well understood. However, it is important to emphasize the effects of certain parameters on pump performance. These effects/parameters include, but are not limited to, the following, in order of strongest dependence wherein pump's operating efficiently is a function of:
1. the pump supply water temperature;
2. the total quantity of water introduced into the pump;
3. the location in the pump where water is introduced; and
4. the cleanliness of the supply water.
Reasons for such importance, and the explanations for these behaviors are:
1. For a given water inflow rate, a pump can handle a certain volumetric rate of gases. With increasing temperature the vapor pressure of water increases thereby increasing the proportion of water vapor contained in the gas mixture which the pump has to move. Therefore, the volume of gases other than water vapor, namely those entering a dentist's handpiece and/or saliva ejector, and which is the volume of gases desired to be moved by the pump, decreases.
2. At a given water temperature, the performance of the pump increases with increasing quantity of water up to some maximum performance for a specific value of water inflow rate. Above that specific water inflow rate, the pump's performance decreases. This is due to the fact that initially, with small water injection rates, a circular ring of water is built up within a cylindrical cavity and the eccentrically mounted impeller outer radius is only partially immersed in the "water ring". As a greater water rate is added, this outer water ring increases in thickness until the impeller outer radius is continuously in contact with the ring of water. It is for this water ring thickness and the corresponding water injection rate that the pump has maximum performance. By injecting more water, the water ring thickens and the gas moving cavities in the impeller decrease in volume, thereby reducing the volumetric rate of gases that can be moved by the pump.
3. Some water ring pumps introduce the water through the intake manifold, others through special water injection ports built into the pump housing and others use a combination of both. The best performance can be achieved by introducing all of the water through the special injection ports in the housing. This is because bringing the water in through the intake manifold reduces the volume of gas that can occupy the inflow area, and increase the drag on the gases desired to be moved, because the added water must be accelerated by the gas flow. Also, the water in the inlet manifold is broken into droplets, increasing the surface area of the water allowing more water to vaporize thereby decreasing the volume of other gases and ergo decreasing the performance of the pump. This situation is exacerbated during the recirculation of water, because recirculated water is by its very nature warmer, and so a compound degradation of performance results.
4. The cleaner the supply water is, the longer the pump will last and the better it will operate. Dirty injection water will cause abrasion of some pump and ducting parts and coating with biological material on others. Abrasion wears parts, thereby increasing critical tolerances between moving parts which decreases performance. Coating of other parts reduces the volumes and areas which increase flow resistance and decrease flow rates, thereby decreased performance. It is therefore important to extract recirculated water in as clean a state as possible.
In existing water recycling systems, the location of recirculated water extraction is typically within a standard sized or an enlarged version of a common plumbing trap of the drainage stream below an "air-water" separator, regardless of the simplicity or sophistication of such an air-water separator. ("Air" in this context refers to any and all gases in the effluent stream including water vapor.) Such traps contain highly agitated and mixed water flows, and in some applications can easily be "blown out" because of an inefficient upstream air water separator. This provides dirty and at times no recirculation flow, but only gas. This sometimes non-existent or otherwise dirty water is typically introduced into some portion of the intake manifold of the vacuum pump.